JPH024688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous spinning method for viscose rayon.

In the continuous spinning method for viscose rayon, the viscose spinning dope is extruded through appropriate spinning projections in a coagulation bath, passed through several coagulation baths for coagulation and stretching, and wound around a device that supports and advances the yarn. Move it almost spirally. During this time, the yarn undergoes sequential processing to impart the desired final properties.

It is well known that these treatments include chemical and/or mechanical treatments, which reduce the sulfur content of the finished product to zero or as low as possible and whiten the yarn color. By the way. Actually, xanthogen oxidation, that is, sulfidation, of alkali cellulose is carried out in the viscose production process, but at this time, sulfur-containing by-products are produced in addition to cellulose ester. During subsequent processing, some of these by-products produce sulfur in addition to carbon disulfide and hydrogen sulfide when they come into contact with the coagulation bath. The presence of elemental sulfur in the fibers of the product is a major drawback, especially during textile dyeing, and increases the sensitivity of the final product to light.

Specifically, the sources of sulfur are, for example, perthiocarbonate (Na ₂ CS _3+X ), sodium thiosulfate (Na ₂ S ₂ O ₃ ), and polysulfides (Na ₂ S _x ).
on the other hand, from the by-products produced during the xanthogen oxidation of alkaline cellulose containing polysulfide chains (-S-S-), and on the other hand from the hydrogen sulfide generated during contact with acidic coagulation baths. , then sulfur is also produced by oxidation. Sulfur produced from compounds with polysulfide chains is dispersed throughout the fiber structure and is therefore very difficult to remove.

Continuous spinning processes for viscose rayon include treatments to eliminate or reduce the sulfur content to a minimum amount. However, the above-mentioned treatment method is difficult to carry out because the time for this treatment, ie the contacting with the respective chemical treatment agent, is very short, especially during high-speed spinning. In addition, in order to carry out different chemical treatments in layers very close to the processing equipment in order to impart different desired properties to the product yarn, a complex process is required to avoid the mixing and spreading of treatment solutions with different chemical compositions. It is necessary to use equipment. The equipment for this is complex and expensive and also consumes large amounts of chemical processing agents.

The main object of the present invention is to provide a process which can eliminate the above-mentioned drawbacks of conventional processes by producing viscose with a low content of sulfur compounds harmful to viscose production.

Another object of the present invention is to provide a simplified method for continuous spinning of viscose rayon, which method is simple as it eliminates complex processing steps to reduce the sulfur content and bleach the product. has been made into

A further object of the invention is to provide a viscose with a low content of compounds capable of forming elemental sulfur, which viscose is particularly suitable as a spinning dope for continuous spinning.

A further salient object of the invention is to provide regenerated cellulose yarns with improved properties in terms of elemental sulfur content and whiteness.

This objective, and rather the objectives to appear in the future, are achieved by the process for producing viscose according to the invention. In the xanthogen oxidation treatment of that method, alkali cellulose is reacted with carbon disulfide in an amount greater than that required to replace xanthate to the desired degree, and when the substitution has progressed to the desired degree, unreacted carbon disulfide is removed under reduced pressure. and remove from the reactor.

In this way, the formation of harmful sulfur compounds that occur as the reaction progresses is suppressed, and the ratio of xanthate-type sulfur to total sulfur is lower than that of conventional xanthate oxidation, that is, the total amount of carbon disulfide added to the reactor. It was found that when , reacts, it becomes larger than , and is therefore advantageous.

Unmentioned features and advantages of the present invention will become apparent from the following detailed description of the invention in its practical implementation.

The main steps in the viscose manufacturing process include the production of alkali cellulose, the production of cellulose xanthate by xanthogen oxidation or sulfurization of alkali cellulose, and the production of the viscose spinning stock solution itself by dissolving the latter in dilute sodium hydroxide solution. Includes generating.

The viscose spinning dope referred to herein is then discharged as yarn from a suitable spinning nub into an acidic coagulation bath to form regenerated cellulose, which is then subjected to suitable post-treatment known in the rayon spinning process to produce the final rayon yarn. occurs.

To carry out xanthogen oxidation according to the method of the invention, a reactor is charged with alkali cellulose that has been carefully degraded and depolymerized to the desired average degree of polymerization. The temperature of the alkali cellulose charged into the reactor is approximately 21°C. The reactor, after purging the interior with inert gas if desired, is placed under vacuum such that the residual pressure within the reactor is 110 mm Hg. Here, carbon disulfide corresponding to 33 to 38% (by weight) of the cellulose in the alkali cellulose is charged into the reactor. The implication is that a 10-25% excess of carbon disulfide is used relative to the amount of carbon disulfide needed to achieve the desired degree of substitution in the xanthate.

Carbon disulfide taken into the reactor evaporates and the residual pressure rises to 400-500 mmHg. Since the reaction is exothermic, the temperature will rise, but it is controlled to be maintained between 23 and 25°C.

The degree of substitution of xanthate when a certain amount of carbon disulfide acts on alkali cellulose of a certain composition at a certain temperature is determined empirically.
When the degree of substitution reaches a desired value after a certain period of reaction, excess carbon disulfide is removed from the reactor by suction and transferred to a recovery device. In this way, the degree of vacuum in the reactor is again virtually equal to that at the beginning.

When operating according to the invention, the reaction space is still under reduced pressure, but an inert gas,
Preferably nitrogen is introduced to remove carbon disulfide,
Avoid the formation of explosive mixtures in the reaction space.

After removing excess carbon disulfide from the reaction space, the viscose production process continues by adding a conventionally measured amount of dilute sodium hydroxide to dissolve the cellulose xanthate and form a viscose spinning stock solution. will be carried out. In this way, a viscose spinning dope is produced, in which the sulfur content derived from by-products capable of producing elemental sulfur is significantly reduced compared to the sulfur content obtained in the conventional viscose production process. It's small.

How the process according to the invention is carried out and what advantages it has will be better understood by the following examples.

A comparative example is provided to illustrate a conventional xanthogen oxidation method.

Example 1 15.4% sodium hydroxide and 31.5% cellulose in a xanthogen oxidation reactor equipped with a mechanical stirrer
Add alkaline cellulose containing.

The pressure in this container is reduced to 160 mmHg. Then nitrogen is introduced to eliminate the vacuum and return to normal pressure. Then, depressurize the container again to reduce the residual pressure to 110mm.
Hg and then introduce carbon disulfide in an amount equivalent to 35% (by weight) of the cellulose in the alkali cellulose at a temperature of about 21°C.

The residual pressure in the reactor rises to about 400 mmHg. The sulfurization reaction continues with stirring for about 110 minutes, during which time the temperature rises to 23°C. Finally, nitrogen is introduced into the reactor to eliminate the vacuum.

Thereafter, the pressure in the container is strongly reduced to approximately 110 mmHg, and the excess carbon disulfide that has not reacted with the alkali cellulose is removed by suction. The suctioned carbon disulfide is recovered.

After the pressure has reached the aforementioned minimum value, a measured amount of sodium hydroxide is added to the reaction vessel to dissolve the cellulose xanthate and prepare a viscose spinning dope.

Next, nitrogen is introduced, the vacuum is stopped, and the viscose spinning stock solution is discharged from the reaction vessel.

The sulfur content of the viscose thus obtained is as follows.

Total sulfur = cellulose in viscose
26% (this value corresponds to the amount of unreacted carbon disulfide, which corresponds to 88% of the carbon disulfide introduced into the reaction vessel).

Sulfur in the xanthate form = 19.5% of the cellulose in viscose Sulfur in the sodium thiocarbonate form = 6.1% of the cellulose in viscose Sulfur in the polysulfide form = 0.09% of the cellulose in viscose Sulfur in the thiosulfate form = viscose 0.29 for the course
% In the previous sulfur content data, the total amount of sulfur contained in compounds with polysulfide bonds, represented by the last two types of sulfur balance, is equal to 0.38% (by weight) of cellulose in viscose.

When regenerated cellulose yarn is spun from the above-mentioned viscose with such a sulfur content, the total sulfur content is 0.15-0.20% based on the weight of the yarn, and the sulfur content is 0.15% to 0.20%, and the sulfur content is 0.15% to 0.20% of the weight of the yarn. Sulfur is 0.03-0.06%.

If such a high sulfur content is to be obtained using conventional methods, the only option is to further de-sulfurize the threads that have come out of the coagulation bath.

Example 2 The procedure was repeated as in Example 1, with the difference that the sulfurization reaction was carried out until a final temperature of 25° C. of the reaction medium was reached. In this case, it stopped after about 80 minutes.

Next, the reduced pressure is removed, and then, as in Example 1, the reaction vessel is suctioned to 120 mmHg to remove excess carbon disulfide.

Continuing the operation further, a sodium hydroxide mixture is introduced into the vessel to prepare a viscose spinning stock solution.

The sulfur content of the viscose obtained according to this example is very close to that obtained in example 1.

Comparative Example Alkaline cellulose with a composition of 16% sodium hydroxide and 31.5% cellulose is placed in a reaction vessel. This reaction vessel is depressurized to a residual pressure of approximately 160 mmHg.
When the temperature is reached, carbon disulfide is added in an amount equivalent to 31.5% of the cellulose content in the alkali cellulose. The residual pressure will be raised to about 600-660mmHg and the temperature will be about 25℃. The total elapsed time of the reaction is approximately 80 minutes. Here, a sodium hydroxide mixture is added to prepare a viscose spinning stock solution.

The reaction produces cellulose xanthate, and the excess carbon disulfide still remaining is absorbed by the sodium hydroxide.

Fill the container with nitrogen, stop the vacuum, and take out the viscose spinning stock solution. Its sulfur content is as follows.

Total sulfur = cellulose in viscose
26% (indicating that 98% of the carbon disulfide used has reacted).

Sulfur in the xanthate form = 18.7% of the cellulose in viscose Sulfur in the sodium thiocarbonate form = 6.9% of the cellulose in viscose Sulfur in the polysulfide form = 0.17% of the cellulose in viscose Sulfur in the thiosulfate form = in viscose As can be seen from the above content, the last two
The sulfur content of the component having a polysulfide bond capable of producing elemental sulfur is 0.56%, which is the same amount as the above-mentioned 2.
The values in the example have increased by almost 50%.

In this case, in order to bring the sulfur content of the yarn produced by spinning this viscose to within the permissible limit, that is, the elemental sulfur content is about 0.03 to 0.06% (weight) of the yarn, de-sulfur treatment is performed. It is necessary to

Proceeding further, the present invention is directed to a method for continuous spinning of viscose obtained by the sulfurization (xanthogen oxidation) method of the present invention. The continuous spinning method according to the present invention is characterized by spinning viscose with a low content of compounds having polysulfide bonds, using appropriate spinning projections, coagulating it in an acidic bath, and not requiring any sulfurization treatment after coagulation. It has Furthermore, due to the properties of the starting material viscose and the small amount of elemental sulfur produced during the coagulation step, the consumption of whitening agent will be low.

Advantageously, the continuous spinning method of the present invention allows for significant savings in processing agents to further reduce the elemental sulfur content and metal content of the spun yarn. In this method, the ash content of the yarn is reduced, the degree of swelling of the yarn removed from the coagulation bath is high, and during the subsequent post-coagulation treatment, the yarn is naturally removed from the bath and from the chemical treatment agent. The degree of swelling decreases. In this way, the permeation conditions created during the swelling of the resulting yarn and the conditions that allow elemental sulfur and heavy metal sulfides to be released from the yarn by osmosis are maintained for as long as possible. The effect of spontaneous removal or release of impurities from the thread section in this post-coagulation stage is asymptotically active. If the post-coagulation time is increased to about 90 seconds, the post-coagulation stage becomes optimal and the impurity content remaining in the final product can be further reduced, 50-60% compared to yarns that do not undergo this post-coagulation treatment. % decrease.

As is clear from what has been said above, all of the objectives are achieved by the method of the invention.
In fact, the present invention allows the production of viscose with a low content of sulfur compounds that tend to form monosulfur during the coagulation stage, making it possible to use continuous spinning methods that do not require mechanical or chemical treatments for desulfurization. It can be significantly simplified.

Additionally, the product's low sulfur content further improves whiteness and reduces the need for bleach. In this way, in the conventional method, various complicated devices were required to separately maintain the processing after coagulation and drawing of the thread, as well as the processing for imparting the necessary properties to the final product. The invention also succeeded in significantly simplifying the continuous spinning device for viscose rayon since these devices were not necessary.

Claims (1)

[Claims] 1. In reacting alkali cellulose with carbon disulfide, after reducing the pressure of a reactor charged with alkali cellulose at a temperature of about 21°C to an initial pressure of about 110 mmHg, about 10
~25% excess carbon disulfide was added until the final pressure was ca.
400 to 500 mmHg and the temperature at the end of the reaction is maintained at about 23 to 25 °C, and once the desired degree of xanthate substitution is reached, the pressure is increased to about 400 to 500 mmHg, equal to the initial pressure without introducing new air. 110mmHg
1. A continuous spinning method for viscose rayon, which comprises obtaining viscose by removing unreacted carbon disulfide from a reactor by reducing the pressure to 100°C, spinning the viscose, and coagulating the thread in an acid bath. 2 providing a post-coagulation stage after the acidic coagulation stage;
A continuous spinning method for viscose rayon according to claim 1, characterized in that the yarn having a high degree of swelling is brought into free contact with a treatment substance at a post-solidification stage without being brought into contact with a chemical treatment agent. . 3. Claims 1 or 2, characterized in that before the pressure is reduced to remove unreacted carbon disulfide, an inert gas is introduced and the pressure is reduced to remove the carbon disulfide. Continuous spinning method for viscose rayon as described in section.